Zinc Porphin Research Articles

Study on the zinc porphyrins as potential carbonic anhydrase mimics for promoting CO2 absorption in K2CO3 solution

Zinc porphyrins, boasting a coordination environment akin to that of natural carbonic anhydrase (CA), coupled with excellent structural stability, built-in hydrophobic pocket, and suitable charge of center Zn2+, were considered as potential CA-mimics for CO2 capture. To validate this assumption, three zinc porphyrin representatives, zinc porphin (ZnP), zinc protoporphyrin IX (ZnPP), and zinc meso-tetrakis(N-methylpyridinium-4-yl) porphyrin (ZnTMPyP), were prepared, and tested performance in enhancing CO2 absorption in water and K2CO3 solutions. The results from CO2 absorption experiments indicated that ZnTMPyP with the optimal dosage increased CO2 absorption rate by 44.25 % in water, and ZnPP with the optimal dosage increased the CO2 absorption rate by 63.67 % in 20 wt% of K2CO3 solution, which are respectively 1.53 and 2.07 times of CO2 absorption performance of zinc cyclen (ZnC), the most effective CA-mimic reported. Besides, the zinc porphyrins demonstrated excellent stability and reusability throughout five cycles of CO2 absorption and desorption, which are vital aspects for practical applications. Through the calorimetric method and density functional theory (DFT) calculations, it was confirmed that the prepared zinc porphyrins had similar enzymatic behavior and catalytic CO2 hydration pathway to natural CA. According to the results of characterization and DFT calculations, high dispersion, the lowest charge of the Zn2+ center, and the existence of additional CO2 adsorption sites (propionate ions), endow ZnPP with the highest catalytic activity in the K2CO3 solution.

Calculation of electron transfer rates in proteins

Electron transfer rates in Zn/Ru modified myoglobins are calculated using a molecular orbital method to obtain the electronic factor and empirical values of the reorganization energy and driving force. The protein is partitioned into three subsystems, A, B, and C, where A and C consist of the metal ions and their ligands and B is the protein bridge between A and C. Molecular orbitals are calculated in each subsystem. Interaction matrix elements between the subsystems are calculated and the total eigenvalue problem solved using a partitioning technique. The distance dependence of the rate is only roughly exponential as a function of intermetal distance. In particular, the rate of the His-12 derivative is larger than the average exponential decrease, in agreement with the experiments. If the indole group in the pathway between the metal ions is replaced by an equally large (CH{sub 2})n-chain, the calculated rate is close to the average exponential decrease. The electronic spectra of zinc porphin (ZnP) and Zn-substituted myoglobin (ZnMb) are calculated using a CNDO/S approach, and the results compare favorably with the corresponding experimental spectra.

Valence ionization potentials and cation radicals of prototype porphyrins. The remarkable performance of nonlocal density functional theory

Nonlocal density functional theory (NLDFT) has been used to calculate the lower ionized states of the free-base forms of porphin, bacteriochlorin, and porphyrazine and also zinc porphin. For porphin, the calculated vertical ionization potentials (IPs) quantitatively reproduce the low-energy end of the experimental gas-phase ultraviolet photoelectron spectrum, which suggests that NLDFT could be an exceptionally useful tool for studying IPs and cation radical states of a variety of porphyrinic materials.

Spectral diffusion of molecular electronic transitions in amorphous solids: Weak and strong two-level-system phonon coupling.

The two-level-system (TLS) model of glasses is used with nonphenomenological TLS distribution functions [R. Jankowiak et al., J. Phys. Chem. 90, 3896 (1986)] to account for the time-dependent spectral-diffusion data for cresyl violet and zinc porphin in ethanol glasses at low temperatures [K. A. Littau and M. D. Fayer, Chem. Phys. Lett. 176, 551 (1991); H. C. Meijers and D. A. Wiersma, Phys. Rev. Lett. 68, 381 (1992)]. The two distributions of faster and slower TLS relaxation rates required to fit the data are characterized for both weak and strong TLS-phonon coupling. Comparison of the values obtained for the TLS parameters with those determined earlier for specific heat, thermal conductivity, pure dephasing, and spontaneous filling of nonphotochemical holes establishes that the faster and slower distributions are associated with intrinsic and extrinsic TLS. The pronounced effects of strong coupling on the TLS relaxation-rate distributions are discussed.

Glass dynamics probed by the long-lived stimulated photon echo.

The dynamics in an ethanol glass at 1.5 K has been investigated from picoseconds to milliseconds by two-dimensional stimulated-photon-echo measurements on zinc porphin. In this time frame the distribution of relaxation rates exhibits a 1/R dependence except for a gap stretching from about 1 kHz to 1 MHz. Evidence is presented for a time evolution of the glass structure that is not accounted for in the standard two-level-system model.

Influence of the experimental parameters on time-resolved transient hole-burning

The influence of the burning power, burning time and probe power on the holewidth, hole depth and hole decay time have been studied in time-resolved transient hole-burning (THB) experiments. The systems investigated are free-base porphin (H 2P) in crystalline n-octane ( n-C 8), zinc-porphin (ZnP) in n-C 8, and ZnP in amorphous polyethylene (PE). The THB kinetics is interpreted in terms of saturation broadening due to a triplet state bottleneck. The holewidth and decay time of the hole are not influenced by the probe power, P p/ A, at least for P p/ A⩽10 μW/mm 2. The same hole-broadening kinetics has been found to apply for the crystalline and the amorphous hosts here studied.

The phosphorescent3Eustate of zinc porphin inn-alkane host crystals

A magnetic resonance study is reported of the 3 Eu state of zinc porphin in an n-octane host in zero field from 1·2 K to 65 K. The temperature dependence is caused by an exchange process between the two orbital components of the 3 Eu state. Spin-lattice relaxation is dominated by thermal excitation to a close lying local phonon state. Crystal field splittings have been determined for the 3 Eu and 1 Eu (S 2) states of zinc porphin in a series of n-alkanes.

Crystal field effects on the vibronic properties of the Jahn–Teller unstable S1 state of zinc porphin

The spacings in the vibrational progression associated with a Jahn–Teller (JT) active normal coordinate in the S1 state of a metalloporphin (MeP) and the intensities and polarizations of the corresponding S1–S0 optical transitions have been calculated as a function of the b1g and b2g strain components (δ1 and δ2 respectively) of the crystal field. The numerical results obtained for the specific case of zinc porphin (ZnP) demonstrate that the vibronic spacing and the optical properties are noticeably affected by the b2g strain component of the crystal field. From previous experimental data on ZnP in the so-called A site of n-octane (n-C8) and n-decane (n-C10) it is deduced that δ2<15 cm−1 (n-C8) and <10 cm−1 (n-C10)≪δ1. A preliminary analysis of the experimental data on ZnP in anthracene demonstrates that here the reverse situation may obtain, i.e., that δ1≪δ2.

Population hole-burning using a triplet reservoir: S 1 ← S 0 transition of zinc porphin in n-octane

Optical hole-burning has been observed in the S 1 ← S 0 absorption of zinc porphin in n-octane by selective depletion of the ground state population and storage in the mestastable triplet state. In this way the homogeneous linewidths of S 1 ← S 0 for molecules in A and B sites of n-octane were measured between 1.6 and 4.5 K. Thermally induced dephasing was observed for B-site molecules with an activation energy of 14 cm −, equal to the separation between the two electronic components of S 1.

The metastable triplet state of zinc porphin and magnesium porphin: A study by E.S.R. in an n-octane crystal at 1·4 K

E.S.R. experiments at 1·3 K are reported for the photo-excited triplet state of zinc porphin (ZnP) and magnesium porphin (MgP) in single crystals of n-octane. The effect of partial and complete deuteriation, and the influence on the E.S.R. spectra of the addition of ethanol or benzene as a second solvent are given. It is found that most of the ZnP molecules occupy one orientation, whereas MgP + ethanol occurs in two orientations for which the molecules are coplanar but differ by a rotation of 90° about the out-of-plane axis. For ZnP, MgP, and free base porphin (H2P) the zero-field principal axes are parallel to within 5° and run through opposite nitrogen atoms. By E.S.R. combined with X-ray diffraction an insight into the orientation of the porphin molecules in the n-octane host is obtained. The fine structure results show a small (ZnP) to negligible (MgP) influence of the spin-orbit coupling of the metal atom. The observed hyperfine structure in ZnP closely resembles that in MgP and originates from four ...

Calculation of the spin density and spin-spin dipolar interaction in the triplet state of metal porphins

The spin density and zero-field splitting (ZFS) of the lowest triplet state of a light metal porphin are determined by means of a Pariser-Parr-Pople ground state SCF π-electron MO-calculation with CI. Only the pz -orbitals of the carbon and nitrogen atoms are considered. The semi-empirical values of the integrals involving nitrogen orbitals are varied between the values commonly used for pyrrole and pyridine-type nitrogen. The two lower triplet states (corresponding to the excitations 3(eg ←a 2u ) and 3(eg ←a 1 u ) in Gouterman's four orbital model) are considered, both for a b 1g and a b 2g the spin densities determined by McLachlan's extended Hartree-Fock method lead to a perfect explanation of the hyperfine structure observed for zinc porphin and magnesium porphin in n-octane. The ZFS parameters are calculated by a semi-empirical method; satisfactory agreement with experiment is obtained only if the CI expansion is truncated at the point where the weight of the individual configurations becomes less th...

Conventional and dye laser optical spectra of zinc porphin in anthracene

Abstract Conventional polarized optical absorption spectra and fluorescence spectra of single crystal and polycrystalline samples of zinc porphin in anthracene have been obtained at 4.2 K. Narrow band excitation of fluorescence using a tunable dye laser was used for site selection to eliminate ambiguities due to impurities and multiple sites. The spectra are compared to those of zinc porphin in a different aromatic host (triphenylene) and in n-octane. Some of the vibronic energies are assigned to calculated vibrations of a similar metalloporphin, copper porphin.

Jahn-Teller instability of the first excited singlet state of zinc porphin: a study by Zeeman spectroscopy in somen-alkane host crystals at 4·2 K

Experiments in a strong magnetic field (7·5 T) have been performed on the S 1 ←S 0 absorption spectrum of zinc porphin (ZnP) at 4·2 K in n-alkane hosts ranging from n-heptane to n-decane, in order to determine the orbital angular momentum Λ, the frequency v, and the distortion parameter α of the active mode of the Jahn-Teller unstable state S 1. Although the crystal-field splitting δ varies strongly for the sites considered (δ = 5–109 cm-1), nearly-constant values for the other three parameters are obtained: Λ = 3.9–4.2, α = 1·1–1·3, and v = 171–180 cm-1. The results prove the validity of the model previously proposed for the Jahn-Teller instability of a metalloporphyrin in a crystal field. A low-frequency mode of 17 cm-1 is observed in the S 1 and S 0 states of ZnP in n-heptane. In the Zeeman spectra it leads to a level anticrossing, and in fluorescence and absorption it shows up in hot bands.

ChemInform Abstract: MAGNETIC CIRCULAR DICHROISM STUDIES. PART 45. A COMPARISION BETWEEN THE MAGNETIC CIRCULAR DICHROISM AND SHPOL′SKII SPECTRA OF PALLADIUM, ZINC, AND MAGNESIUM PORPHIN

Chemischer InformationsdienstVolume 8, Issue 18 Physical Organic Chemistry ChemInform Abstract: MAGNETIC CIRCULAR DICHROISM STUDIES. PART 45. A COMPARISION BETWEEN THE MAGNETIC CIRCULAR DICHROISM AND SHPOL′SKII SPECTRA OF PALLADIUM, ZINC, AND MAGNESIUM PORPHIN G. BARTH, G. BARTHSearch for more papers by this authorR. E. LINDER, R. E. LINDERSearch for more papers by this authorN. WAESPE-SARCEVIC, N. WAESPE-SARCEVICSearch for more papers by this authorE. BUNNENBERG, E. BUNNENBERGSearch for more papers by this authorC. DJERASSI, C. DJERASSISearch for more papers by this authorY. J. ARONOWITZ, Y. J. ARONOWITZSearch for more papers by this authorM. GOUTERMAN, M. GOUTERMANSearch for more papers by this author G. BARTH, G. BARTHSearch for more papers by this authorR. E. LINDER, R. E. LINDERSearch for more papers by this authorN. WAESPE-SARCEVIC, N. WAESPE-SARCEVICSearch for more papers by this authorE. BUNNENBERG, E. BUNNENBERGSearch for more papers by this authorC. DJERASSI, C. DJERASSISearch for more papers by this authorY. J. ARONOWITZ, Y. J. ARONOWITZSearch for more papers by this authorM. GOUTERMAN, M. GOUTERMANSearch for more papers by this author First published: May 3, 1977 https://doi.org/10.1002/chin.197718050AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume8, Issue18May 3, 1977 RelatedInformation

MCD of transitions to Jahn-Teller unstable states in the metalloporphins of Mg, Zn, Cu, Pd and Pt

MCD spectra of solutions of magnesium, zinc, copper, palladium and platinum porphin in EPA measured at 77 K are reported and analysed. It is concluded from the experimental data that the Jahn-Teller (JT) coupling in the first excited singlet states S 1 of palladium porphin (PdP) and platinum porphin (PtP) is very weak but that it is sizable in zinc porphin (ZnP). The JT-active mode of ZnP is identified with the 170–180 cm-1 vibration of this molecule. For the JT-distortion parameter α we find for PdP and PtP: α<0·3 and for ZnP: α=1·2±0·3. For the orbital angular momentum Λħ in the S 1 state we find for PdP and PtP: Λ=(4·0±0·4) and for ZnP: Λ = (3·7±0·4). From the value of the A-type MCD integrated over the whole S 1-S 0 absorption band it is deduced that in PdP 40 per cent of the intensity in this band is induced by b-type vibrations and 20 per cent by a-type vibrations. For PtP these figures amount to 30 per cent and 20 per cent. Analysis of the MCD spectra with the help of the dispersion method reveals ...

High resolution spectra of zinc porphin and magnesium porphin in a n-octane matrix at 4.2 K. Effect of the addition of ethanol and other solvents

Addition of solvent with free electron pairs on oxygen or nitrogen (ethanol, D 2O, diethyl ether and pyridine) to zinc porphin (ZnP) in n-octane crystals causes the appearance of new spectra in absorption, flourescence and phosphorescence, superimposed on the normal ligand-free ZnP spectrum which has its origin at 17,954 cm −1 (absorption and flourescence) and 14,671 cm −1 (phosphorescence). The origins of the new spectra are displaced by 300–900 cm −1 to lower energy as compared to the normal spectrum. With ethanol and D 2O the line widths of the origins are the same as observed for the normal spectra (<3 cm −1, whereas with diethyl ether and pyridine much broader lines result. Magnesium porphin in n-octane shows complicated spectra with many origins in the region 17,300–17,500 cm −1. After addition of ethanol a single spectrum remains with its origin at 17,415 cm −1 (absorption and flourescence). Microwave transitions between the spin components of the lowest triplet state have been used to distinguish between the solvated and unsolvated ZnP molecules.

PHOTOREDUCTION OF ZINC PORPHIN BY ASCORBIC ACID*

Abstract— Zinc porphin is photoreduced to zinc chlorin through an intermediate dihydroporphin (PH2) by ascorbic acid in ethanol containing 1% to 10% (v/v) piperidine. Under the same conditions zinc chlorin is more slowly photoreduced to zinc tetrahydroporphin. The reactions leading to chlorin are photosensitized by the product chlorin and so are autocatalytic in red light. Quantum yields for these reactions range up to 0.05.Other aliphatic amines catalyze these reactions, but at rates peculiar to the amine. The immediate product of reduction of zinc porphin, PH2, is distinguished by an intense band at 437 nm; it reverts to porphin in the dark in the presence of oxygen or dehydroascorbic acid. Its conversion to chlorin is effected by light absorbed by porphin or chlorin, but not by light absorbed by PH2 itself. A suggested structure for PH2, compatible with the observed reactions, has added hydrogens on one bridge carbon and one β‐pyrrole carbon. The possibility of an analogy between these reactions and the biochemical conversion of protochlorophyll to chlorophyll is discussed.